Conventionally, a rotary-type fluid machine is known which includes an eccentric-rotation type piston mechanism having a cylinder formed with a cylinder chamber and a piston housed eccentrically in the cylinder chamber. In the rotary-type fluid machine, one of the cylinder and the piston is formed as a fixed member and the other thereof is formed as a moving member attached eccentrically to a drive shaft, and the drive shaft is rotated to thereby rotate the moving member eccentrically to the fixed member.
In the rotary-type fluid machine, the drive shaft rotates while undergoing a periodic variation in the output torque thereof, and the variation in the output torque may cause a vibration or a noise in the rotary-type fluid machine.
Japanese Patent No. 3757977 discloses a rotary-type fluid machine capable of suppressing a variation in the output torque thereof. The rotary-type fluid machine is configured as a rotary compressor and includes two eccentric-rotation type piston mechanisms arranged vertically in tiers, each having two compression chambers on the same plane.
Specifically, an eccentric-rotation type piston mechanism (60) described above is formed, as shown in FIG. 12, with a compression chamber (C1, C2) and a piston (61) each having a ring shape. The ring-shaped piston (61) is housed eccentrically in the ring-shaped compression chamber (C1, C2) of a cylinder (62) such that the compression chamber (C1, C2) is partitioned into an outside compression chamber (C1) and an inside compression chamber (C2). The cylinder (62) is provided with a blade (63) partitioning each of the outside compression chamber (C1) and the inside compression chamber (C2) into a high-pressure side (Hp) and a low-pressure side (Lp). The cylinder (62) as a moving member is rotated eccentrically to the ring-shaped piston (61) as a fixed member.
Here, the piston (61) is housed in a cylinder chamber (C1, C2, C3, C4) such that as the cylinder (62) is eccentrically rotated, a phase difference of 180 degrees in volume change is made between the outside compression chamber (C1) and the inside compression chamber (C2).
FIG. 13 is a graphical representation showing how a variation in the rotation angle of a drive shaft affects the output torque of the drive shaft. In the figure, a line A indicates a variation in the total output torque of the drive shaft by the outside compression chamber (C1) and the inside compression chamber (C2), a line B indicates a variation in the output torque of the drive shaft by the outside compression chamber (C1, C3) and a line C indicates a variation in the output torque of the drive shaft by the inside compression chamber (C2, C4).
The phase difference in volume change between the outside compression chamber (C1) and the inside compression chamber (C2) is shifted by 180 degrees, and thereby, the peak values of the output torque of the drive shaft by each compression chamber (C1, C2) are also shifted by 180 degrees. Therefore, the eccentric-rotation type piston mechanism (60) generates output-torque variations (the lines B and C of FIG. 13) where the peak values by each compression chamber (C1, C2) alternately appear at intervals of 180 degrees.
Then, the output-torque variations by each compression chamber (C1, C2) affect each other, and thereby, the eccentric-rotation type piston mechanism (60) is capable of generating the total output torque of the drive shaft shown by the line A of FIG. 13 and suppressing a variation in the output torque of the drive shaft.
In the rotary compressor according to Japanese Patent No. 3757977, the two eccentric-rotation type piston mechanisms capable of suppressing an output-torque variation in this manner are arranged vertically in tiers, and a phase difference of 90 degrees in volume change is made between the cylinder chambers (C1, C2, C3, C4) of both eccentric-rotation type piston mechanisms (20). Specifically, the eccentricity directions of the rotation axes of both cylinders fixed to the drive shaft mutually have an angle difference of 90 degrees to the axial center of the drive shaft.
Similarly to FIG. 13, FIG. 14 is a graphical representation showing how a variation in the rotation angle of a drive shaft affects the output torque of the drive shaft. In the figure, a line B indicates a variation in the output torque of the drive shaft in the case of only the upper eccentric-rotation type piston mechanism (20), a line C indicates a variation in the output torque of the drive shaft in the case of only the lower eccentric-rotation type piston mechanism (20) and a line A indicates a variation in the output torque of the drive shaft in the case where the upper and lower eccentric-rotation type piston mechanisms (20) are joined together.
The rotational phases of both eccentric-rotation type piston mechanisms (20) are mutually shifted by 90 degrees, and thereby, the peak values of the output torque of the drive shaft by each eccentric-rotation type piston mechanism (20) are also shifted by 90 degrees. Therefore, the rotary compressor according to Japanese Patent No. 3757977 generates output-torque variations (the lines B and C of FIG. 14) where peak values (P1, P2, P3, P4) by each compression chamber (C1, C2) of each eccentric-rotation type piston mechanism (20) appear at intervals of 90 degrees.
Specifically, the peak value (P1) by the inside compression chamber (C2) of the upper eccentric-rotation type piston mechanism (20), the peak value (P3) by the inside compression chamber (C2) of the lower eccentric-rotation type piston mechanism (20), the peak value (P2) by the outside compression chamber (C1) of the upper eccentric-rotation type piston mechanism (20) and the peak value (P4) by the outside compression chamber (C1) of the lower eccentric-rotation type piston mechanism (20) appear at intervals of 90 degrees in this order.
Then, the output-torque variations by the two eccentric-rotation type piston mechanisms (20) affect each other, and thereby, the rotary compressor is capable of generating the total output torque of the drive shaft shown by the line A of FIG. 14 and further suppressing a variation in the output torque of the drive shaft.